The present invention refers to a railway axle hub unit of the type comprising an axle box housing for supporting a bearing.
Mechanical deterioration of the axle supporting bearings, besides adversely affecting the operational performance of the axle, also reduces the safety of the vehicle and may lead to the failure of the bearing, with catastrophic consequences such as derailment.
The main structural or functional defects which bearings of the above kind or the relative wheel are subject to can be summarised as follows:
manufacturing or assembling defects of the bearing, which provoke an excessive play between its components (inner and outer raceways, rolling bodies, retaining cages, sealing devices, shoulders defining the axial position of the bearing with respect to the axle); cracks or spalls due to fatigue; local pitting due to an electrical current passing through the bearing; rust marks;
insufficient lubrication of the inner parts of the bearing; polluted or deteriorated lubricant;
flats in the rolling surface of a wheel due to the wheel being locked while the railway vehicle is travelling; excessive wear of the wheel profile in the rail contact zone;
axial play of the wheel with respect to the axle, whereby the rotation axis of the wheel is not perpendicular to a vertical plane.
Up to now methods of checking the conditions of the bearings have been limited to periodical maintenance interventions. With such interventions, all the bearings of a same vehicle are replaced regardless of their conditions, including bearings being still valid and not needing to be replaced.
It will be understood that this way of proceeding first of all involves high costs of labour and passive costs for leaving the vehicle unused, but above all it does not allow to predict or detect the occurrence of failures in time before the bearing is so deteriorated to represent a condition of potential danger. Therefore, there is the risk of continuing to use a defective bearing or wheel for prolonged periods till the moment set by the maintenance schedule for replacement.
U.S. Pat. No. 5,433,111 discloses an apparatus for detecting defective conditions associated with a set of railway vehicle wheels and with a railtrack upon which a given railway vehicle travels. The apparatus comprises measurement means for generating data indicative of rotational rate of the wheels, a set of accelerometers adapted to generate data indicative of motion along three orthogonal axes, wherein one of the axes is generally vertical with respect to the railtrack, and a data processor adapted to detect, based on the received rotational rate and motion data, a defective condition associated with at least one wheel of the vehicle.
U.S. Pat. No. 5,381,692 refers to a monitoring system of a bearing assembly for supporting the drive shaft of a helicopter. The system has a vibration sensor for providing signals indicative of the vibrations emanating from the bearing assembly, first temperature sensing means for providing signals indicative of the bearing assembly operating temperature and second temperature sensing means for providing signals indicative of the ambient temperature. An alarm subsystem in response to the vibration and temperature signals provides an alarm signal warning of degradation condition of the bearing.
It is an object of the present invention to predict and/or identify in time and give a warning of the presence of a defect, the kind of defect and its precise location, in particular distinguishing which wheel of the vehicle or train is affected by the defect, and more particularly distinguishing whether the defect is affecting the wheel, its bearing or one of the components of the latter.
Another object of the present invention is to provide a continuous and real time monitoring of the operating condition of the bearing to obtain real time information concerning the variation of the defect in time, so that it is possible to intervene with urgency for severe failures, or delay intervention depending on the gravity of the detected failure, or consider the opportunity of not intervening, for example when an operation defect is stabilised or is stabilising.
Another object of the invention is to optimise maintenance, so as to intervene only when it is appropriate or necessary, and replace only the bearing individuated as defected or worn out.
These and other objects, which will be better understood herein after, are achieved according to the present invention by a railway axle hub unit of the type comprising an axle box housing for supporting a bearing, characterised by being equipped with sensor means for detecting vibration in a generally vertical direction, said sensor means being mounted onto a stationary support element rigidly secured to the bearing, said sensor means being adapted for generating and transmitting signals indicative of the detected level of vibration to an electronic processing unit on board of the railway vehicle or the train, whereby said processing unit is capable of signalling in real time an impending failure and/or a damaged condition associated with said monitored hub unit.
A further object of the invention is to provide a hub unit equipped with vibration sensors located at an optimal position for detecting the vibrations which the bearing and the wheel are subjected to, and for individuating correctly the nature, the location and the extent of possible defects.
This object is accomplished by a hub unit having the features defined in claims 2 to 4.
Further important features are defined in the other depending claims.